Derail/diːˈreɪl/ Definition 1 of 3Pro Tip 1/3Literal Usage Used when something, usually a train, physically goes off its track. Heavy snowfall made the cargo train derail near the mountain pass. Pro Tip 2/3Unexpected Events Refers to accidents caused by unexpected events, not just weather. A rockslide is another natural incident that could derail a train. Pro Tip 3/3Emergency Response Emphasizes the emergency action taken after an incident of this nature. Rescue teams were immediately dispatched to help after the derailment.